The women, who underwent biopsies in two Nottinghamshire hospitals between 2004 and 2010, were given the wrong information on what type of breast cancer they had.

Managers at Sherwood Forest NHS Foundation Trust, which runs Newark and King’s Mill hospitals, have apologised to the 79 surviving women and invited them back for an “urgent review” of their treatment.

The women were wrongly told they had oestrogen-receptor negative breast cancer, when they were actually oestrogen-receptor positive. It is thought an error in preparing the slides containing breast cancer tissue was to blame.

An external panel, asked to review the situation, estimated about half the 120 consequently received sub-optimal treatment.

The panel concluded the affected women had a five per cent increased chance of dying from breast cancer over 10 years as a result.

Dr Nabeel Ali, executive medical director, said: “We have contacted all the women affected by these pathology errors to apologise unreservedly for the error which has occurred, and we will be in touch with the next of kin of any who have since died.”

Two health regulators, the Care Quality Commission (CQC) and Monitor, announced on Monday they were taking action to look at how the trust was running the two hospitals.

Last year it spent £42.5 million - or £1 in every six - on PFI payments for the £320 million King’s Mill Hospital in Sutton-in-Ashfield, which was completed in 2010. In the first quarter of this financial year the trust lost £5.9 million.

The CQC has launched an “urgent inspection” of breast cancer screening, pathology and clinical governance, plus a wider investigation of patient care called a “deep dive review”.

Monitor, which regulates semi-independent foundation trusts, has ordered Sherwood to commission a series of reviews because it is concerned the board has “failed to get to grips with the scale of the problems it faces”.

These will examine how well it is governed and whether it is financially viable in the long term.

Last month Dr David Bennett, chief executive of Monitor, told MPs that Sherwood Forest was one of just two foundation trusts whose “underlying” financial problems were caused by its PFI debts.

Days later Monitor sent board members a letter telling them to expect regulatory action, because its finances were deteriorating.

David Behan, chief executive of the CQC, said the joint action would enable both regulators to "have a good picture of the quality and safety of the trust’s services and the robustness of its governance".

Stephen Hay, chief operating officer of Monitor, said: “We are using our formal regulatory powers of intervention because we are concerned the trust has failed to get to grips with the scale of the problems it faces."

“In addition to the trust’s financial difficulties our concern about its leadership has been heightened by the disclosure that some breast cancer patients are to receive an apology from the trust and an urgent review of their treatment after an investigation into faulty pathology test results.”

Gloria de Piero, the Labour MP for Ashfield, said she was “deeply concerned” about the situation.